Groups of individuals, such as police officers, firefighters, rescue workers or soldiers, often need to conduct operations in built up urban areas. While operating in such areas, the individuals often find it difficult or impossible to maintain accurate and updated knowledge of one another's locations because the structures in an urban area block visual contact between the individuals. As a result of the inability to establish visual contact, soldiers in urban environments often become casualties of friendly fire. Similarly, police officers, firefighters and soldiers are not able to assist fallen comrades who may be nearby, yet cannot be visually observed.
Current electronic position location systems do not provide a satisfactory solution to the problem of providing an individual, who is part of a group of individuals, with current information as to the absolute positions of other individuals in the group when the individuals of the group are located in an urban environment where visual contact among and between individuals of the group is difficult or not possible. For example, the well known global positioning system (“GPS”), which includes orbitting GPS satellites that transmit positioning information signals for receipt by a GPS enabled communications device on land, provides that a GPS enabled communications device can compute its absolute position (“GPS fix”), in terms of latitude, longitude and altitude, based on receipt of GPS information signals transmitted from the GPS satellites. Based on currently available GPS fix computation techniques, however, a GPS enabled communications device can compute its GPS fix only if it can receive GPS information signals transmitted from at least four GPS satellites.
In urban areas, an individual carrying a GPS enabled device often moves to locations that do not permit the GPS enabled device to receive GPS information signals transmitted from at least four GPS satellites. For example, natural terrain or man-made structures in an urban environment often attenuate or block signals transmitted from GPS satellites. Therefore, a group of individuals, each carrying a GPS enabled device, cannot always rely upon the computation of a GPS fix at each individual of the group, and the communication of the GPS fix from one individual to other individuals of the group, such as by wireless means, to ensure that each individual of the group continuously is aware of the absolute positions of other individuals in the group.
Therefore, a need exists for system and method for determining the absolute positions of individuals who are members of a group, where none of the individuals of the group can receive remote positioning information signals transmitted more than three remote positioning information signal transmission sources, such as GPS satellites, to permit a communications device carried by an individual of the group to determine its absolute position solely based on the remote positioning information signals that it can receive.